not found while looking for property

最近在研究hibernate。过程当中碰到了很多问题啊！其中一个就是not found while looking for property错误

Caused by: org.hibernate.MappingException: class main.Java.POJO.User not found while looking for property: id

配置文件如下：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC
        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
        "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="main.java.POJO">
<class name="User" table="loginuser">
     <id name="id" column="Id" >
         <generator class="native"/>
     </id>
     <property name="username" column="username"  />
     <property name="password" column="password" />
     <property name="sex" column="sex"  />
</class>
</hibernate-mapping>

怎么看配置也没有问题啊！网上找了N久！终于在这篇文章里面看到了原因！

按照里面的方法把每个值都加上属性后就OK了

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC
        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
        "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="main.java.POJO">
<class name="User" table="loginuser">
     <id name="id" column="Id"  type="java.lang.Integer">
         <generator class="native"/>
     </id>
     <property name="username" column="username"  type="java.lang.String"/>
     <property name="password" column="password"  type="java.lang.String"/>
     <property name="sex" column="sex"  type="java.lang.String"/>
</class>
</hibernate-mapping>

特记于此！以备勿忘！